First off, thank you very much for doing this. It's been on my TODO list for a bit (just further down the stack).

A few questions:

have you tested this out with gcc?

have you built this on all architectures (I might have a valid "make universe" environment on universe12a... that could be used)?

Not yet; I opened the code review in parallel with build testing. But I'm definitely going to do a full universe on this one.

Also:

could you please move this down the WARNS assignment above the first set of .includes?

What?

Per style.Makefile(5), WARNS should come before CFLAGS/CXXFLAGS (I misremembered that nuance too so I'm guilty of getting it wrong, probably). Not a ship blocker, but if we can nip this in the bud now, that would be awesome :)... (Either way, I'm ok with the change as-is, because it's a net win :)..)!